This invention relates to arrays manufactured on polymeric surfaces and more particularly to high-density, miniaturized arrays and methods of manufacturing the same.
Miniaturized arrays may be used in a variety of applications, such as gene sequencing, monitoring gene expression, gene mapping, bacterial identification, drug discovery, and combinatorial chemistry. Many of these applications involve expensive and oftentimes difficult to obtain samples and reagents. Accordingly, high density, miniaturized arrays are desirable because the use of such arrays may dramatically increase efficiency with respect to limited or expensive samples when compared to standard arrays, such as a 96 well plate. For example, a 96 well plate may require several hundred microliters of sample per well to run a diagnostic experiment whereas a miniaturized array would require only a fraction of that sample for the entire array. In addition to the reduction of volume, miniaturization allows hundreds or thousands of tests to be performed simultaneously. Furthermore, a high-density array may be more versatile than a standard array because of the wide variation of chemistries that may be present on a single array.
Current methods of manufacturing miniaturized arrays are not conducive to mass production. These methods are limited by multiple step procedures and by the difficulty in achieving miniaturized arrays with densely packed reactants. The manufacture of arrays is further complicated in applications requiring different chemistries at different binding sites on the arrays, such as required for manufacturing oligonucleotide arrays.
One example of a multiple step procedure for manufacturing arrays is disclosed in U.S. Pat. No. 5,445,934. This patent discloses a method of on-chip synthesis. In this process, the substrate is derivatized with a chemical species containing a photocleavable protecting group. Selected sites are deprotected by irradiation through a mask. These sites are then reacted with a DNA monomer containing a photoprotective group. The process of masking, deprotecting and reacting is repeated for each monomer attached until an array of site-specific sequences is achieved. This process may be both time-consuming and resource intensive. Because of the planar nature of the surface, a limited concentration of oligonucleotides (measured by the distance between adjacent oligonucleotides within a binding site) can be synthesized at each binding site before steric crowding interferes with the hybridization reaction. As a result, the amount of detectable signal from each binding site may also be limited.
Another type of method used to manufacture arrays is off-chip synthesis. An example of off-chip synthesis is disclosed in U.S. Pat. No. 5,552,270. This process uses gel pads. The gel pads are created on a substrate using robotic devices. Thereafter, minute quantities of presynthesized oligonucleotides are robotically placed on individual gel pads on the substrate. Production of chips using off-chip synthesis is generally time-consuming because each solution is deposited individually or in small groups. High densities are difficult to achieve because of the limited resolution of robotic devices and the physical size limitations of the fluid delivery devices. This type of process typically requires the use of specialized, sophisticated, and miniaturized tools. The use of gel pads facilitates the affixation of a higher concentration of oligonucleotides within each binding site, which may overcome the difficulties encountered with planar surfaces outlined above. However, the use of thick gel layers hinders hybridization kinetics due to slow target analyte diffusion into and out of the gel.
There is a need for high density, miniaturized arrays including reactive surfaces with high surface areas and high detection signal strength. Preferably, the arrays would facilitate rapid binding kinetics between affixed reactants and target analytes. There is a further need for methods of manufacturing high density, miniaturized arrays. The methods preferably would be cost-effective and amenable to mass production.
In one embodiment of the present invention, an array includes a polymeric substrate and a coating comprising linking agents at least partially adhered thereto. The coating comprising linking agents has a projected surface area and a topographical surface area, and the topographical surface area is greater than the projected surface area. The topographical surface area is at least two times greater than the projected surface area. In a preferred embodiment, the topographical surface area is at least five times greater than the projected surface area. In a most preferred embodiment, the topographical surface area is at least fifteen times greater than the projected surface area. Preferably, the coating includes an undulated surface.
In a preferred embodiment of the present invention, the array includes a binding site density of over 1,000 binding sites per square centimeter. A density of at least 25,000 binding sites per square centimeter is preferred with a density of over 60,000 per square centimeter being most preferred.
In another embodiment of the present invention, a material for use in manufacturing an array includes an oriented, polymeric substrate including a coating comprising linking agents. This material is suitable for the subsequent affixation of reactants thereto.
The arrays of the present invention facilitate the affixation of a high concentration of reactants at each binding site, with all of the attendant advantages of high density, including the ability to increase detection signal strength. The high topographical surface area arrays are particularly useful in this regard. In addition, these high surface area arrays allow sample containing the analyte(s) of interest to rapidly come into contact with the reactants, without the necessity of diffusing into a thick coating, such as a hydrogel.
In one embodiment of the methods of the present invention, a polymeric substrate includes a major surface having a surface area. A reactant, such as DNA, is affixed to the major surface of the substrate to create binding sites. The surface area of the major surface is reduced, thereby increasing the density of binding sites on the substrate.
In a preferred embodiment, the substrate is a biaxially oriented, heat shrink film. In a particularly preferred embodiment of the present invention, the reactants are oligonucleotides wherein the oligonucleotides vary in composition at differing binding sites on the substrate.
In another method of the present invention, a heat shrink film is finctionalized to create linking agents on the surface of the film for subsequent attachment of reactants. The surface area of the substrate surface may be reduced, thereby increasing the density of linking agents on the substrate. Preferably, the heat shrink surface is functionalized with azlactone linking agents.
In yet another embodiment of the present invention, an elastomeric substrate is stretched and functionalized to create linking agents on the surface of the substrate. Reactants, such as DNA, may be affixed to the substrate via linking agents. The substrate is subsequently allowed to relax, thereby reducing the surface area of the substrate to increase the density of linking agents on the substrate. A backing or other structure may be added to retain the substrate in the reduced orientation.
In yet another embodiment of the present invention, a method of manufacturing arrays of the present invention includes providing an oriented polymeric substrate. A coating comprising linking agents is applied to a surface of the substrate. Subsequently, the substrate is relaxed such that it becomes less oriented or isotropic. During this relaxation step, the topographical surface area of the coating becomes greater than the projected surface area of the coating. Reactants may be affixed to the linking agents prior, during or subsequent to the relaxation step to create an array with binding sites. Preferably, the reactants are affixed prior to the relaxation step.
The methods of manufacture of the present invention are amenable to mass production. The methods of manufacture of the present invention may be employed to increase the efficiency of current methods of manufacture of arrays to achieve high densities of reactants. The methods of the present invention are particularly useful in achieving high-density nucleic acid arrays wherein different nucleic acids are located at different sites on the substrate.
Various other features and advantages of the present invention should become readily apparent with reference to the following detailed description, examples, claims and appended drawings.